This invention relates to electrostatographic printing machines, and more particularly to an electrostatographic printing machine wherein toner images deposited on an intermediate belt are transferred with a high percentage of efficiency to a transfuse belt used for simultaneously transferring and fusing toner images to various substrate media such as plain paper.
Electrostatographic printers are known in which a single color toner image is electrostatically formed on a charge retentive member such as a photoreceptor drum or belt. The toner image is directly transferred to a receiving substrate, typically paper or other suitable print receiving material. The toner image is subsequently fused or affixed to the substrate, usually by the simultaneous application of heat and pressure.
In other electrostatographic color printers, a plurality of toner imaging systems each including a charge retentive member are used to create multiple color toner images on a single image receiving member. The color toner images are electrostatically transferred from the charge retentive members to an intermediate transfer member to form a composite toner image on the intermediate transfer member. The intermediate transfer member could be an Intermediate Transfer Belt (ITB) or an intermediate transfer drum. The composite toner image is electrostatically transferred to the final substrate. Such systems that use electrostatic transfer to transfer the composite toner image from the intermediate belt to the final substrate and then subsequently fix the image on the substrate in a fusing system have transfer limitations. For example, there are limitations due to stresses introduced with rougher paper stock, foils, paper moisture content variations, etc. Also, the need to electrostatically transfer a fully layered color composite toner image to the substrate creates additional high stresses for electrostatic transfer. Stressful system conditions can include, for example, systems that use papers at wide ranges of relative humidity, and systems that create images on a large range of paper size and thickness. Such stresses can adversely affect transfer due to their effect on the electrostatic transfer fields, and they can also have significant effect on paper transport.
In addition with direct transfer to paper from an imaging module, is fibers, talc and other particulate debris or chemical contaminants can readily transfer from the paper to the imaging modules during direct contact in the electrostatic transfer zones. This tends to contaminate the imaging medium, development systems, cleaner systems, etc., and can lead to early failure of the such systems. This is especially true for certain stress inherent paper types including, for example, certain types of recycled papers. Due to all these and other problems, systems that use direct transfer to the final media generally have narrow media latitude for obtaining and/or for maintaining high print quality.
Alternatively, in another prior art printer, a toner image is formed on a photoreceptor. The toner image is transferred to a single intermediate transfer member usually referred to as a transfuse member. The transfuse member generally simultaneously transfers and fuses the toner image to a substrate. The use of a single transfer member in a transfuse system can result in high transfer efficiency of background toner on the photoreceptor to the substrate due to high adhesion between the toner and typical materials used for the transfuse member, such as silicone materials. In addition, oil oligomer is generally present or else added onto silicone or other materials used for transfuse members to assist toner release to paper under the high temperature conditions used for eventual transfer and fix of the image from the transfuse member to the final receiver substrate. The photoreceptor can be contaminated by heat and oil on the transfuse member via the transfer nip.
To overcome some of the deficiencies of these single transfer and double-transfer arrangements, prior systems have employed two transfer belts. Toner images are formed on photoreceptors and transferred to a first or intermediate transfer belt. The toner images are subsequently transferred to a second transfer member such as a transfuse belt.
Transfer of toner images has been addressed in many different ways as depicted in the patents noted below and incorporated herein by reference. In addition to possibly having some relevance to the question of patentability of the present invention, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 6,088,565 granted to Jia et al on Jul. 11, 2000, discloses an electrostatographic printing machine that has multiple toner image producing stations, each forming a developed toner image of a component color. The developed toner images are electrostatically transferred at the first transfer nip to an intermediate transfer member to form a composite toner image thereon. Rheological assisted electrostatic transfer transfers the composite toner image at a second transfer nip to a transfuse member. The transfuse member preferably has improved conformability and other properties for improved transfusion of the composite toner image to a substrate. The transfuse member is maintained above the glass transition temperature of the composite toner image at the second transfer nip. The composite toner image and the substrate are brought together in a third transfer nip to simultaneously transfer the composite toner image and fuse the composite toner image to the substrate to form a final document.
U.S. Pat. No. 5,119,140 granted to Berkes et al on Jun. 2, 1992 discloses a method and apparatus wherein very efficient transfer of low toner masses from an intermediate image receiving member without degradation of high toner mass transfer is achieved using DC pretransfer corotron treatment of the toner on the intermediate followed by biased roll transfer to plain paper. U.S. Pat. No. 4,341,455 (Fedder), discloses an apparatus for transferring magnetic and conducting toner from a dielectric surface to plain paper by interposing a dielectric belt mechanism between the dielectric surface of an imaging drum and a plain paper substrate such that the toner is first transferred to the dielectric belt and subsequently transferred to a plain paper in a fusing station. The dielectric belt is preferably a material such as Teflon or polyethylene to which toner particles will not stick as they are fused in the heat-fuser station.
U.S. Pat. No. 5,612,773 granted to Berkes et al Mar. 18, 1997 discloses a transfusing member having a compression layer comprised of a highly conformable, low durometer material with a low surface free energy. The transfusing member forms a first transfer nip characterized by a first pressure with a photoreceptive surface and a second transfer nip characterized by a second pressure, which is of the same order of magnitude as the first pressure, with a backup roller.
U.S. Pat. No. 5,805,967 granted to DeBock et al on Sep. 8, 1998 discloses single-pass, multi-color electrostatographic printer has a transfer member that is driven along a continuous path. Toner images of different colors are simultaneously electrostatically deposited in powder form in registration with each other on the transfer member to form a multiple-layered toner image. The substrate is fed into contact with the transfer member for transfer of the multiple-layered toner image to at least one face of the substrate. The printer includes a heater for the multiple-layered toner image on the transfer member in advance of the transfer of the image to the substrate, and cooling capability for the transfer member following the transfer of the multiple toner image to the substrate, to a temperature below the glass transition temperature, Tg of the toner, prior to deposition of further toner images on the transfer member. The second transfer member is cooled below the glass transition temperature of the toner prior to the transfer nip with the first transfer belt. Cooling of the second transfer belt requires the second transfer member to be relatively thin. A thin second transfer belt however has low conformance therefore providing reduced transfer efficiency when rougher paper or other media is in the transfuse nip. The reduced conformance also increases the potential for undesirable xe2x80x9cdifferential glossxe2x80x9d, which is high glossing when high toner mass per unit area types of color images are in the transfuse nip but relatively much lower glossing when low toner mass per area images are in the transfuse nip. In addition, a thin second transfer belt can have a reduced operational life.
U.S. Pat. No. 5,452,063 granted to Gerald M. Fletcher on Sep. 19, 1995 discloses an image forming apparatus using intermediate image transfer with high humidity papers wherein a toned image is formed on an image receiving member. The image forming apparatus includes an intermediate belt, at least one image forming device, and a transferring device. In one embodiment, the intermediate belt includes a conductive substrate and a topcoat insulating layer to receive the toned image so as to avoid lateral conduction of charges. In another embodiment, the image forming apparatus includes an intermediate belt having a semiconductive substrate and biasing means for biasing a transfer zone, pre-transfer zone and post-transfer area of the substrate.
U.S. Pat. No. 5.671,472 granted to Christopher Snelling on Sep. 23, 1997 discloses apparatus for forming toner images on an image receiving member and transferring the toner images from an image receiving member to copy sheets including a transfer intermediate member s having piezoelectric properties for transferring the images from the image receiving member to the transfer intermediate member and subsequently transferring the images from said transfer intermediate member to copy sheets.
U.S. Pat. No. 5,890,045 granted to Till et al on Mar. 30, 1999 discloses a method for transporting a developed image from a moving image bearing member to a moving copy substrate, comprising the steps of transferring the developed image from the moving image bearing member to a moving intermediate transfer member including an elastic belt at a first nip formed between the moving image bearing member and the moving intermediate member; transferring the developed image from the moving intermediate transfer member to the copy substrate at a second nip formed between the moving intermediate member and the moving copy substrate; transporting the moving image bearing member and the moving intermediate member at a substantiality equivalent first velocity in the first nip; and transporting the intermediate member and the moving copy substrate at a substantiality equivalent second velocity different from the first velocity in the second nip.
As can be appreciated from a consideration of the above-mentioned patents, problems inherent in toner image transfer from belt structures has not been accomplished, for the most part, without the use of devices associated with the belt for effecting such transfer and/or complicated belt configurations. In addition to the highly efficient transfer of toner images from an intermediate belt, it is also desirable to prevent any release agent material utilized in the printing process from being deposited on imaging members such as photoreceptor drums.
Pursuant to the intents and purposes of the present invention, the Intermediate Transfer Belt (ITB) presented here has a surface that is fabricated to enable very high image transfer efficiency, i.e. a transfer efficiency nearly equal to 100%. Additionally, the ITB surface is effective in allowing only minimal deposition of release agent materials from the ITB onto photoreceptor surfaces.
To the foregoing ends, the surface of the belt is roughened such that the wavelength of the roughness is in the order of 20 nanometer to 3 xcexcm and the peak to valley vertical distance is in the order of 20 nanometer to 5 xcexcm.
The specified belt surface roughness minimizes the contact area between the toner particles and the ITB surface. The minimized contact area between toner particles and belt surface reduces the amount of electrostatic transfer field required. This enables high fidelity transfer from the ITB to paper and other image receiving media or from the ITB to a transfuse belt. While The ITB surface is roughened it is macroscopically smooth in order to avoid air-breakdown problems in the nip and pre-nip regions.
Another advantage of the roughened belt surface is that less oil is transferred from the print media or transfuse member to the ITB and less oil is transferred from the ITB to the photoreceptor. For example, with a single intermediate belt system that uses electrostatic transfer from the intermediate to the final print media and then fuses the toner in a fusing system, oil can be transferred to the print media in the fuser and carried back to the intermediate during transfer in a duplex mode. This can have adverse effects on transfer off of or onto the intermediate, and the oil can be carried to the imaging modules during subsequent contact between the intermediate and the imaging stations. For a single intermediate belt transfuse system, oil can be directly transferred to the imaging systems during contact of the ITB with the transfuse member. For a two belt transfuse system, oil from the transfuse member can transfer to the intermediate transfer member and subsequently transfer oil to the imaging systems from the first intermediate transfer member. The microscopically bumpy surface of the intermediate transfer member reduces the amount of oil transfer from the intermediate transfer member to the imaging systems. In addition, in a two belt transfuse system the microscopically bumpy surface of the intermediate transfer member reduces oil transfer from the transfuse member to the intermediate transfer member, and in a single intermediate belt system it reduces the amount of oil transfer from duplex print media to the intermediate transfer member.
Still another advantage is that friction forces on a blade cleaner are reduced resulting in longer belt and blade life.
Yet another advantage of a roughened or bumpy belt surface is the reduction of frictional forces on the transfer nips, thereby facilitating smooth separation of the intermediate from the imaging stations and allowing better stripping of print media from the intermediate, and also thereby reducing motion disturbances in the imaging system and reducing registration problems.
The bumpy aspects of the belt are effected by the addition of low surface energy, high Young""s modulus particles to the material utilized for the fabrication of the belt. The particles are dispersed substantially uniformly through the belt thickness such that when particles occupying the top-most surface of a new belt are worn away particles that lie beneath those particles then occupy the top-most surface of the belt. Thus, the bumpy feature of the belt surface is continually renewed. Alternatively, the rigid particles are dispersed only on the topmost layer of the intermediate transfer member.